Determination of trace amounts of Pb, Cd, Ni and Co by wavelength-dispersive X-ray fluorescence spectrometry after preconcentration with dithizone functionalized graphene

In this paper, a new simple and sensitive method is developed for the preconcentration of trace amounts of lead (Pb), cadmium (Cd), nickel (Ni) and cobalt (Co) ions using graphene as a solid sorbent. It was found that functionalizing graphene with dithizone could greatly improve the preconcentration capability of graphene. After sorption, the graphene adsorbed with the metal ions was collected onto a filter, and then the preconcentrated elements were directly determined by wavelength-dispersive X-ray fluorescence spectrometry (WDXRF). With the dithizone functionalized graphene, excellent enrichment factors ranging from 926 to 985 were obtained for Pb2+, Cd2+, Ni2+ and Co2+. Parameters affecting the extraction process (pH of the analyte solution, stirring time, the volume of the sample, complexing agent, adsorption capacity), and the effect of foreign metals were evaluated. Under optimum conditions, the calibration graphs were linear in the range of 0.01 mu g mL(-1) to 3.0 mu g mL(-1) with a correlation coefficient better than 0.99, detection limits of Pb2+, Cd2+, Ni2+ and Co2+ were 2.0 ng mL(-1), 6.1 ng mL(-1), 1.1 ng mL(-1), and 1.3 ng mL(-1), respectively. Quantitative recoveries (> 95%) were obtained for all four studied metal ions. The proposed method was successfully applied to measure the trace amounts of Pb2+, Cd2+, Ni2+ and Co2+ in different types of environmental water samples, and the relative expanded uncertainty of measurement of these four ions is smaller by 16%.